In a number of industrial applications, it is the practice to transport large quantities of finely divided materials, granular or otherwise, such as chopped up fiber glass strand, in containers like standard corrugated cardboard boxes that open towards the top or the bottom and contain 700 kg or more of material.
The use of cardboard boxes opening towards the top is only partly suitable to such heavy loads because it is necessary to use costly equipment in order to invert and unload their contents into mill hoppers or mixng apparatus. For this reason, various types of containers, formed especially of cardboard, are available which are made to open from the bottom; their lower part, is frequently reinforced by extra thickness or by a wooden floor, and are formed into a pallet assembly on their lower side to allow handling. Such arrangements usually include interlocking tongues or flaps that can be folded up into a closed position along a separation line generally provided with a glued tear-strip or with perforations, or small releasable tongues, and for emptying purposes, a passage or even a funnel, usually situated in the center. Usually, these costly and relatively fragile containers can be reused only a few times.
It must be noted that the larger the said passage, the less the stiffness remaining in the container during the emptying operations; moreover, there is a risk of incorrect draining by premature rupture of the locking mechanism in the course of handling.
On receptacles of substantial size, the passage size must be proportionally reduced, with the result that the emptying will often be incomplete because pockets of the material tend to form in dead zones, particularly in the corners. A more serious disadvantage is that a certain number of substances present flow difficulties because of their inherent nature. This is especially true of fibrous materials. During the unloading of a container which only partially opens at the base, bunching can form arches in the inside causing cessation of the unloading, especially if the passage is relatively narrow.